Conventionally, rubber products such as tires, rubber hoses, industrial belts, vibration insulating rubbers, fenders, and shoe soles are produced using rubber compositions containing diene rubbers.
As an example of a rubber composition which may be used in such applications, a rubber composition formed by compounding from 1 to 50 parts by weight of a modified polymer, which is prepared by modifying a polyolefin resin with an unsaturated carboxylic acid, with 100 parts by weight of a diene rubber has been proposed (Japanese Unexamined Patent Application Publication No. 10-87900).
On the other hand, when a rubber composition is used for sidewalls, there is a demand for excellent ozone resistance. Therefore, natural rubbers and butadiene rubbers are typically used as rubber components in a rubber composition for sidewalls. However, when a natural rubber and a butadiene rubber are used in combination, there is a problem in that the tensile properties (modulus, elongation at break) are diminished in comparison to when only a natural rubber is used (Comparative Example 1).
Under such circumstances, when a rubber composition containing a diene rubber and an acid-modified polyolefin was prepared and evaluated using Japanese Unexamined Patent Application Publication No. 10-87900 as a reference, it is clear that there is room to improve the tensile properties in order to use a rubber obtained from such a rubber composition as a sidewall (Comparative Examples 5 and 4).
In addition, it is clear that there are cases in which the processability is diminished (Comparative Example 3) or the tensile properties are diminished (Comparative Example 2) in a rubber composition containing a diene rubber and a specific acid-modified polyolefin.